What is FDDI (Fiber Distributed Data Interface)?

FDDI (Fiber Distributed Data Interface) is a set of ISO and ANSI standards for data transmission in a wide area or local area computer networks via fiber optic cable.

What is FDDI (Fiber Distributed Data Interface)?

FDDI (Fiber Distributed Data Interface)

FDDI technology was developed in the mid-1980s to augment the capabilities of existing Ethernet and Token Ring technologies and to support high-speed workstations.

In FDDI, data transfer is done with a star topology and double coin ring logic transmitting clockwise or counterclockwise. It also offers 100 Mbps speeds at distances up to 200 meters and supports up to 1000 stations.

It uses backbone technology to connect LANs made of copper cables, or high-speed computers, and traffic on each ring goes in the opposite direction.

Ring connection consists of two or more point-to-point structures between adjacent stations and has two types of linkage, primary and secondary.

The primary ring is used for data transfer, while the secondary ring is often used as a backup link.

There are two types of connection classes in an FDDI network, Class A and Class B. In Class A, computers are connected to both rings. In Class B, computers are connected to a single ring.

SASs are connected to the primary ring with an FDDI hub device that provides connectivity for multiple SAS. The hub keeps the ring running in the event of a power outage or failure in any SAS.

FDDI networks use a transmission mechanism similar to the Token Ring networks. Real-time separation of the network’s bandwidth is achieved with the Synchronous and Asynchronous traffic structure.

In synchronous traffic, part of the total 100 Mbps bandwidth of an FDDI network is used, while in asynchronous traffic the rest is used.

Synchronous bandwidth is assigned to computers that require continuous transmission capacity, enabling more efficient transmission of audio and video information. The remaining bandwidth is used for asynchronous data traffic.

In addition, the priority system can block computers that cannot use synchronized bandwidth and have very low asynchronous priority.

FDDI does not use the Manchester coding system but uses a coding scheme called a 4B/5B scheme where 5 bits are used. Therefore, sixteen combinations enable data transmission, while others perform the control process.

A station can create a new frame without waiting for the return of the data frame, so several frames can be present in the ring at the same time.

The signal technology used for transceivers consists of LED and Laser. While LEDs are generally used for data transmission between computers, the Laser system is used for the backbone system.


FDDI creates a 100 Mbps two-ring LAN with token transmission using a fiber optic transmission medium.

The FDDI network is similar to Token Ring, so both network configurations share certain characteristics such as topologies and media access methods.

One of the main features of FDDI is that it uses fiber optics as the transmission medium, and this offers many advantages over traditional copper cable.

There are two types of fiber, single-mode and multimode. Single-mode fiber allows only one light mode to pass through, while multi-mode fiber allows multiple light modes to pass through.

Since the modes are shown as beams of light entering the fiber at a certain angle, when multiple light modes are propagated through the fiber, they can support different distances depending on the angle of entry.

Single-mode fiber supports higher bandwidth and allows the use of longer cable than multi-mode fiber.

Because of these properties, single-mode fiber is often used in indoor connections. Multimode fiber is mostly used in indoor connection structure.

FDDI basically consists of one fiber optic ring per token pass. Ring topology is physically implemented by fiber optics.

When a node detects this frame and has data to transmit, it grabs the frame by removing it from the ring and releases it when it expires. FDDI provides high-speed interconnection between LAN and WAN networks.

Frame Structure

Frameworks in FDDI technology have a specific structure and each framework consists of the following areas:

   Start Limiter

It indicates the beginning of a frame and consists of signaling patterns that distinguish it from the rest of the frame.

   Frame Check

It contains asynchronous or synchronous data of the frame, control information, and size of address fields.

   Destination Address

It contains the physical address of the target machine, which can be a unicast, multicast, or broadcast address.

   Source Address

It contains a 6-byte source address that contains the physical address of the machine that sent the frame.

   FCS (Frame Check Sequence)

FCS is the area that completes the starting station with a computed redundancy check based on the content of the frame. The target station recalculates the value to determine if the frame was corrupted during transport.

   End Limiter

It contains symbols indicating the end of the frame.

   Frame Status

It allows the source station to determine if there is an error and whether the receiving station has recognized the frame or copied it.

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